The present invention relates to articles having a fine uneven structure on the surface, particularly optical micro-elements and information recording medium substrates, to a production process.therefor and to a composition therefor.
Optical parts such as a diffraction optical element, Fresnel lens and flat microlens (an.array of a large number of microlenses arranged in parallel on a plate), CD-ROM and other information recording media have a fine uneven structure on the surface. This fine uneven structure on the surface serves as a diffraction grating or microlens to converge or diffuse light in optical articles or serves as a pit or tracking guide in an information recording medium.
To form this fine uneven structure on the surface, there are known the following conventional processes (1) to (4).
(1) JP-A 63-49702 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a process in which an ultraviolet curable resin is uniformly spread over a substrate and irradiated with ultraviolet light while a mold having an uneven portion is pressed against the resin.
(2) JP-A 62-102445 discloses a process in which an uneven portion is formed in accordance with a so-called sol-gel method by coating a glass substrate with a solution containing silicon alkoxide and heating while a mold having an uneven portion is pressed.
(3) JP-A 6-242303 discloses a process in which a plurality of layers having a thickness of several micrometers are formed on a substrate by a sol-gel method. In this case, the constituent components of each layer are prepared in the form of a solution or sol and heated while a mold is pressed, and then a solution or sol is poured onto the completely solidified layer to form an upper layer.
(4) J. Am. Ceram. Soc. Vol. 81, No. 11, pp. 2849 and 2852 (1998) discloses a process for producing an optical disk having a fine groove structure by coating a substrate with a solution containing methyltriethoxysilane and tetraethoxysilane.
However, the above prior arts have the following problems. First, in the above process (1), the ultraviolet curable resin decomposes or yellows at a temperature of 250xc2x0 C. or more due to its low heat resistance. Therefore, a substrate having an uneven portion of an ultraviolet curable resin cannot be subjected to a heat treatment such as soldering and it is difficult to install the substrate in an apparatus.
In contrast to this, the uneven portion of silicone alkoxide formed by the sol-gel method in the process (2) has high heat resistance and can be soldered. However, this sol-gel method involves such a problem that a thick film cannot be formed. When a silicon alkoxide layer having a thickness of several micrometers is formed by this sol-gel method in fact, a fine crack is formed on the surface. This is because large stress is generated on the surface due to a difference in the progress of a polycondensation reaction between the surface and the interior of the layer when the silicon alkoxide solution is gelled and solidified. Further, this stress may cause the layer to peel off from the substrate.
The above process (3) is a process for forming a plurality of organopolysiloxane layers sequentially, which is capable of forming an organopolysiloxane layer having an uneven surface and a thickness-of several tens of microns. However, the production process takes long, thereby boosting costs. Further, as a solution for forming the next layer is poured after the underlying layer is completely cured, unnecessary air is easily contained between the mold and the solution or sol, thereby reducing the dimensional accuracy of the uneven portion.
Further, the above process (4) is capable of producing an optical disk whose sol-gel film has a maximum thickness smaller than 300 nm. However, this process involves such a problem that a film is cracked when the film is heated at a temperature required for soldering, for example, 350xc2x0 C. and then cooled to form a diffraction optical element having a film thickness of 500 nm to several micrometers, for example.
It is an object of the present invention which has been made in view of the above problems, of the prior art to provide a process for producing an article having a fine uneven surface which has high heat resistance, does not crack even when it is a single layer film having a thickness of 500 nm (0.5 xcexcm) to several micrometers, does not peel off from a substrate and has high dimensional accuracy.
It is another object of the present invention to provide articles having an uneven surface produced by the process of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
Firstly, according to the present invention, the above objects and advantages of the present invention are attained by a process for producing an article having an uneven surface, comprising disposing a film-forming solution between a substrate and a mold in the form of a film so as to make the solution closely contact with the substrate and the mold, said solution being prepared by carrying out the hydrolysis and dehydration condensation reaction of a stock solution containing a silane compound (A) represented by the following chemical formula (1):
RSiX3xe2x80x83xe2x80x83(1)
wherein R is a non-hydrolyzable organic group and X is a hydrolyzable group,
a silane compound (B) represented by the following chemical formula (2):
SiXxe2x80x24xe2x80x83xe2x80x83(2)
wherein Xxe2x80x2 is a hydrolyzable group,
and a catalyst, and heating to form an article having an article having an uneven film having a surface shape which is the inversion of the surface shape of the mold on the surface of the substrate, wherein
the film-forming solution contains the silane compounds (A) and (B) in the form of unydrolyzates in amounts of 0.5 to 40 wt % and 0.5 to. 60 wt % based on the amount of the silane compound (A) and the amount of the silane compound (B) contained in the stock solution, respectively, and a condensate produced by the dehydration condensation reaction in the film-forming solution has a molecular weight of 300 to 1,900.